1. Field of the Invention
This invention relates to a method for producing a molded article of thin wall thickness from a resin composition comprising a polyolefin and an inorganic filler.
2. Description of the Prior Art
Improvement of the rigidity, thermal stability, dimensional stability, incinerability, etc. of polyolefins by incorporating inorganic fillers has been extensively investigated and, in various fields, has already been achieved to a practical degree. In molding of polyolefins containing inorganic fillers, various methods such as extrusion molding and injection molding have been investigated. In extrusion molding, the addition of an inorganic filler increases the melt viscosity of the polyolefin and the moldability of the filler-containing polyolefin is better than that of the polyolefin alone. As a result, extrusion molding of inorganic filler-incorporated polyolefins has made great achievements in the field of sheet materials, etc.
On the other hand, in injection molding, the increase in melt viscosity brought about by the addition of inorganic fillers is not advantageous and tends to result in more short shots (i.e., incomplete injections) than in the case of molding the polyolefin alone. Attempts to avoid short shots by increasing the molding temperature and the injection pressure results in a tendency to ward mold flashing. Thus, the range of molding conditions which afford good products is extremely limited and, for certain desired configurations, products of good quality cannot be obtained. Accordingly, in the field of injection molding, inorganic filler-incorporated polyolefins have not been considered suitable for the production of articles having complicated configurations or articles having a thin wall thickness. The application of filler-incorporated polyolefins have thus been greatly limited in spite of their better rigidity, thermal stability and dimensional stability in comparison to polyolefins alone.